Multiple slot coating hoppers are known in the art, first being described in the patents of T. A. Russell (U.S. Pat. Nos. 2,761,791 2,761,417). Shown in these patents are hoppers which contain multiple precision metering slots, formed between adjoining plates, for the purpose of simultaneously delivering multiple layers of fluid in large widths, while maintaining uniform thickness of those layers across their width.
More recent art, British Patent 1,389,074 has disclosed that within the coating hopper there may be more than one distribution channel, or cavity, and more than one metering slot used to evenly distribute each fluid layer.
In manufacturing photosensitive products many demands may be placed upon the coating hopper. It is very important that the coating hopper be able to coat many different photographic products. This demands that it be easy, quick, simple, and efficient to changeover from coating one product to coating the next. Additionally, in coating many different products it is important that it be simple to change the width of the metering slots, and hence the coating, to meet the coating width needs of each product. Moreover, it is important that the hopper meet all these demands while maintaining a high level of quality in the coatings. Specifically this means that the width wise uniformity of the small metering slot be maintained. Also this means that it must be possible and easy to clean the entire hopper between products including removing any dirt or particles from the interior spaces of the hopper. These last considerations are important to prevent any contamination between the coating fluids of successive products and to prevent any defects in the coating.
There are several pieces of prior art which provide partial solutions to these multiple needs. U.S. Pat. No. 1,643,643 shows a mechanism installed in the head box slot of a paper mill machine. Although this mechanism provides the ability to adjust the width of the metering slot, it does not provide the ability to fully clean the interior of the hopper without disassembly. There are stagnant spaces behind this mechanism, and it would require taking the hopper apart to fully clean the interior. This does not meet the demand of product changeover efficiency as described above.
Alternatively, in U.S. Pat. No. 2,923,971 provides a description of inserts within the distribution cavity in order to prevent stagnant spaces. This feature may be helpful in preventing the accumulation of fluid, the settling of particles, and may aid in cleaning between products. However, this patent shows no means of changing the metering widths of the fluids to meet individual product coating widths.
U.S. Pat. Nos. 3,870,454 and 4,057,385, describe adjustable deckle blades in extrusion hoppers for the purpose of adjusting the width while preventing leakage past the deckles. These deckle blades are lacking in that they are not easily removable for cleaning between products leaving a severe quality and contamination concern.